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The world’s first identified ocean “dead zone”—a watery region where a combo of nitrogen and phosphorous fertilizer runoff creates monstrous algae blooms that kill off everything in the water—was discovered more than 40 years ago at the mouth of the Mississippi River in the Gulf of Mexico. Today, more than 400 dead zones are growing around the globe; the number has doubled every decade.

No fish can live in the dead zones where fertilizer-polluted rivers dump into the sea. (Photo: Ho New/Reuters)

All of the oceans, say the study authors, have numerous dead zones, with particular hotspots in the tropical South Pacific, off southeastern Australia and China, in the Gulf of Mexico and off Namibia, in the Bay of Bengal, in the Baltic and Black seas and in the South Atlantic. Essentially, the problem exists everywhere rivers meet the sea.

Each spring and summer, the original dead zone in the Gulf of Mexico grows to roughly the size of New Jersey, spanning the ocean from Mississippi to Texas. Nothing in its reach can grow. Around the world, dead zones range in size from one square mile to 27,000 square miles. All told, dead zones now cover nearly 100,000 square miles of ocean, an area larger than the state of Oregon.

Why the boom? A familiar trio of problems: overfishing, nutrient runoff, and climate change. Too many people live and pollute too close to the sea and take its biggest resource (fish) without pondering the consequences.

According to the Australian report, now is not the first time the oceans have died off: “Declining oxygen concentrations have played a major role in at least four or five mass extinction events.” Those were due to meteor strikes or booms in erupting volcanoes, which killed off 90 percent of life in the ocean.

The authors of the new report believe that a similar loss of life could occur in the next 100 years.

“Climate change is driving changes to water circulation—so winds, strange weather patterns, have a consequence for how the ocean turns over and aerates and so on, and it’s the winds which are delivering a lot of organic compounds into the deep sea.

“At the same time, we are putting a lot of fertilizer off coastlines, those sorts of things are incubating these deep water anoxic zones.”

This would be the first time that the ocean died due to man’s influence; as the ocean warms due to a fast-changing climate these low oxygen zones will move closer to the surface and spread out along the continental shelves.

“Ocean ecosystems are in a lot of trouble and it all bears the hallmarks of human interference,” says the study. “We are changing the way the Earth’s oceans work, shifting them to entirely new states, which we have not seen before.”

“It’s mucking around with the heart and lungs of the planet—that’s essentially what the oceans are, a huge respiratory system. We damage them, the consequences could be very serious.”

Last season, during the BP spill, that very first dead zone in the Gulf of Mexico swelled to near-record size. With all that crude polluting the Gulf, could the dead zone get any deader?

Australian scientists fear the planet is on the brink of another mass extinction as ocean dead zones continue to grow in size and number.

More than 400 ocean dead zones – areas so low in oxygen that sea life cannot survive – have been reported by oceanographers around the world between 2000 and 2008.

That is compared with 300 in the 1990s and 120 in the 1980s.

Professor Ove Hoegh-Guldberg, of the ARC Centre of Excellence for Coral Reef Studies (CoECRS) and from the University of Queensland, says there is growing evidence that declining oxygen levels in the ocean have played a major role in at least four of the planet’s five mass extinctions.

“Until recently the best hypothesis for them was a meteor strike,” he said.

“So 65 million years ago they’ve got very good evidence … all the dinosaurs died because of smoke and stuff in the atmosphere from a meteor strike.

“But with the four other mass extinction events, one of the best explanations now is that these periods were preceded by an increase of volcanic activity, and that volcanic activity caused a change in ocean circulation.

“Just as we are seeing at a smaller scale today, huge parts of the ocean became anoxic at depth.

“The consequence of that is that you had increased amounts of rotten egg gas, hydrogen sulfide, going up into the atmosphere, and that is thought to be what may have caused some of these other extinction events.”

Professor Hoegh-Guldberg says up to 90 per cent of life has perished in previous mass extinctions and that a similar loss of life could occur in the next 100 years.

“We’re already having another mass extinction due to humans wiping out life and so on, but it looks like it could get as high as those previous events,” he said.

“So it’s the combination of this alteration to coastlines, climate change and everything, that has a lot of us worried we are going to drive the sixth extinction event and it will happen over the next 100 years because we are interfering with the things that keep species alive.

“Ocean ecosystems are in a lot of trouble and it all bears the hallmarks of human interference.

“We are changing the way the Earth’s oceans work, shifting them to entirely new states, which we have not seen before.”

He says while it is impossible to predict the future, in a century from now the world will be vastly different.

“A world without the Great Barrier Reef, where you don’t have the pleasure of going to see wild places any more,” he said.

“We might be able to struggle on with much lower population densities, but ultimately it won’t be the world we have today.

“The idea of walking in the Daintree will be a forgotten concept because these changes have occurred.”

The image of an ocean dead zone is stark: a barren, underwater desert of silt, littered with the bodies of suffocated crabs and asphyxiated fish.

Caused when agricultural runoff feeds huge algae blooms that suck oxygen out of the water when they decay, so-called hypoxic zones are increasingly common in U.S. waters, a recent government study finds.

The problem is so sweeping that it now affects all of the nation’s coasts and even the Great Lakes, AOL’s David Knowles reports. Climate change is also suspected to be a factor.

The Gulf of Mexico dead zone is the largest and best known, caused mainly by runoff spewing out of the Mississippi. The zone was predicted to spread over an area up to 7,800 square miles in 2010, putting it about the size of New Jersey.

Waters off of Oregon and Washington are perhaps the most in trouble, constituting the third-largest seasonal dead zone in the world, Knowles writes.

Dead zones are also on the rise globally, according to Helium. The number of dead zones worldwide increased from 146 in 2004 to 405 in 2008.

In U.S. waters, the report mainly blames the rise in industrial agriculture for the increase in hypoxic areas. Efforts to stem the activity “have not made significant headway,” a release on the report reads.

“It is imperative that we move forward to better understand and prevent hypoxic events, which threaten all our coasts,” wrote experts in a letter accompanying the report.

The largest dead zone in the world is in the Baltic Sea, where the oxygen depleted waters stretch to the size of Denmark.